Our laboratory investigates the electronic state of atomic or molecular structure in materials using a high resolution double-crystal x-ray spectrometer in order to elucidate the relationship between their structures and physical properties. Our main themes are (1) experimental and theoretical studies on the natural line widths of the elements in materials (Physical Review A 94 042506 and Physical Review A 97 052505), and (2) the development of the four-crystal x-ray spectrometer for the absolute measurements of the diagram lines.